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1Vector Control Research Centre, Indian Council of Medical Research, Indira Nagar, Puducherry 605006, India. gprabha_99@yahoo.com
Abstract:
Immobilized techniques have been used widely for the controlled release formulation of mosquitoes. Among the microbial formulations, polymeric matrices play an important role in the controlled release of microbial pesticide at rates sufficiently effective to kill mosquitoes in the field. The advantage of these matrices is that they enhance the stability of both spores and toxin against pH, temperature variations, and UV irradiation. The disadvantage of using calcium alginate beads is that they are unstable upon contact with phosphate of potassium or sodium ions rich in the mosquito habitats. To overcome these problems, attempts were made to encapsulate Bacillus thuringiensis var. israelensis within alginate by using different multivalent counterions, namely, calcium chloride, zinc sulfate, copper sulfate, cobalt chloride, and ferric chloride, and the beads formed were tested for its mosquito larvicidal activity. Among all the beads tested, zinc alginate beads resulted in maximum larvicidal activity of 98% (+/-1.40 SE) against Culex quinquefasciatus IIIrd instar larvae and maximum spore count of 3.36 x 10(5) (+/-5291.50 SE) CFU/ml. Zinc alginate beads maintained their structure for up to 48 h when shaken vigorously on a rotary shaker at 180 rpm in the presence of 10 mM potassium phosphate buffer (pH 6.8 +/- 0.1). In conclusion, our results suggest that the use of zinc sulfate as counterions to encapsulate B. thuringiensis var. israelensis within alginate may be a potent mosquito control program in the habitats where more phosphate ions are present.
Insights
Zinc alginate beads show enhanced stability and 98% larvicidal activity against Culex quinquefasciatus. This formulation offers a potent mosquito control solution, especially in phosphate-rich environments.
Area of Science:
- Environmental Science
- Microbiology
- Materials Science
Background:
- Polymeric matrices are crucial for controlled release of microbial pesticides, enhancing stability against environmental factors.
- Calcium alginate beads, commonly used, exhibit instability in phosphate-rich mosquito habitats.
- Bacillus thuringiensis var. israelensis is a microbial pesticide used for mosquito control.
Purpose of the Study:
- To develop a more stable controlled-release formulation of Bacillus thuringiensis var. israelensis.
- To evaluate the efficacy of alginate beads encapsulated with different multivalent counterions against mosquito larvae.
- To identify a formulation resistant to phosphate ions found in natural mosquito habitats.
Main Methods:
- Encapsulation of Bacillus thuringiensis var. israelensis spores within alginate beads using various multivalent counterions: calcium chloride, zinc sulfate, copper sulfate, cobalt chloride, and ferric chloride.
- Testing the mosquito larvicidal activity of the formed beads against Culex quinquefasciatus IIIrd instar larvae.
- Assessing the stability of the beads in a phosphate buffer solution under vigorous shaking conditions.
Main Results:
- Zinc alginate beads demonstrated the highest larvicidal activity (98%) against Culex quinquefasciatus.
- The zinc alginate formulation maintained a high spore count (3.36 x 10^5 CFU/ml).
- Zinc alginate beads showed structural stability for up to 48 hours in 10 mM potassium phosphate buffer (pH 6.8).
Conclusions:
- Zinc sulfate as a counterion provides enhanced stability and efficacy for Bacillus thuringiensis var. israelensis encapsulated alginate beads.
- Zinc alginate beads represent a promising strategy for mosquito control, particularly in environments with high phosphate ion concentrations.
- This improved formulation can contribute to more effective and sustainable mosquito population management programs.
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